Vehicles may be fitted with evaporative emission control systems to reduce the release of fuel vapors to the atmosphere. For example, vaporized hydrocarbons (HCs) from a fuel tank may be stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the fuel vapors. At a later time, the evaporative emission control system may purge the stored fuel vapors from the fuel vapor canister into the engine intake. The fuel vapors may then be consumed during combustion.
During a canister purge operation, a canister purge valve coupled between the engine intake and the fuel vapor canister is opened, allowing for intake manifold vacuum to be applied to the fuel vapor canister. Simultaneously, a canister vent valve coupled between the fuel vapor canister and atmosphere is opened, allowing for fresh air to enter the canister. This configuration facilitates desorption of stored fuel vapors from the adsorbent in the canister, regenerating the adsorptive material for further fuel vapor adsorption.
However, hybrid vehicles and other low-manifold vacuum vehicles may have limited engine run-time with sufficient manifold vacuum to execute a purging operation. Herein, a duration of purge operation may not achieve adequate desorption of stored fuel vapors from the fuel vapor canister. As such, if the fuel vapor canister is not completely purged, exhaust hydrocarbons may slip into the atmosphere, degrading exhaust emissions and making the vehicle emissions non-compliant. In addition, the low vacuum may increase engine operation time in a hybrid vehicle in order to purge the fuel vapor canister. The unintended increase in engine run time for the hybrid vehicle can degrade vehicle fuel economy.
The inventors herein have recognized the above issues and have developed systems and methods to at least partially address them. In one example, a method may comprise flowing fuel vapors from a fuel tank through a full length of a fuel vapor canister from a first input to a first output on a first opposite side from the first input, and purging the fuel vapors from the fuel vapor canister through a full width in the fuel vapor canister from a second input to a second output on a second opposite side from the second input. In this way, a fuel system canister can be purged in a shorter duration since the flow directions of the purging and storing are oblique with respect to one another and of different effective lengths, in one example. Further, storage flow may be along only a single path without multiple internal blocking check valves in parallel, whereas purge flow may include a plurality of parallel flow paths via internal blocking check valves and apertures each positioned in parallel.
For example, a fuel vapor canister comprising adsorptive material may be fluidically coupled to a fuel tank via a first input. Fuel vapors received from the fuel tank may flow from the first input to a first output through an entire length of the fuel vapor canister. For example, the first output may be located directly opposite from the first input such that the entire length of the canister is encompassed between the first input and the first output. When purging conditions are met, a canister vent valve may be opened to enable atmospheric air to enter the canister through a second input and desorb stored fuel vapors from within the adsorbent in the canister. The atmospheric air may purge the desorbed fuel vapors through a full width of the fuel vapor canister by flowing from the second input to a second output. Herein, the second output of the canister may be positioned directly across from the second input such that the full width of the canister is encompassed between the second input and the second output. As such, the entire length of the canister may be greater than the full width of the canister. Thus, fuel vapors from the fuel tank may flow through a longer distance (entire length) for adsorption and desorbed fuel vapors may flow across a shorter distance (full width) during purging operation.
In this way, a canister may be quickly and sufficiently purged by reducing a length of purge flow. By flowing the fuel vapors through a longer portion of the adsorbent, a larger proportion of fuel vapors may be adsorbed within the canister. Further, as the adsorbed vapors are purged across a shorter width of the canister, fuel vapors may be expelled more rapidly from the canister, and a duration to purge the canister may be lowered. Furthermore, the likelihood of bleed emissions from the canister may be reduced by enabling a more complete purge of the canister. Overall, exhaust emissions and emissions compliance may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.